The present invention is generally directed to color pixel configurations of a single picture element which are useful in color liquid crystal display (LCD) devices to improve visual perception. More particularly, the present invention is directed to a color pixel configuration which consumes a minimal amount of display area for electrical drive lines and the like, while still providing optimal visual clarity.
In liquid crystal display devices of the matrix addressed variety, liquid crystal material is disposed between panels which are typically glass and in which at least one of the panels and its associated circuitry is transparent. Transparency is achieved by the utilization of metallization connections using materials such as indium tin oxide (ITO). One of the panels typically possesses an array of pixel electrodes, each of which is associated with a switching device which operates to supply an electrical voltage to the pixel electrode. The switching devices preferably comprise thin film amorphous silicon field effect transistors (FETs). The opposing panel possesses a ground plane electrode so that in effect, a capacitor-like structure is established with liquid crystal material being disposed between a "ground plane", or "back plane", electrode and an array of individually controllable pixel electrodes. By switching the associated semiconductor devices, voltages are applied to the pixel electrodes so as to change the orientation and optical properties of liquid crystal material disposed between individual pixel electrodes and the ground plane electrode. In this way, images are constructed on the flat panel device as a configuration of pixel elements. It is noted that variable-magnitude voltage signals by variable magnitude applied to select pixel electrodes can achieve gray scale effects. Signal values large enough to drive the liquid crystal material fully on or off are also employable, particularly in situations in which only character or textual information is to be displayed.
Liquid crystal display devices of the matrix-addressed kind typically include a set of source (or data) lines and a set of gate lines arranged in a rectangular grid fashion so that by application of appropriate electrical signals on the source lines and gate lines, individual pixel electrodes may be controlled so as to produce the desired optical effect, namely the display of part of an image on the screen. Taken in toto, the pixel elements portray the desired image. Thus, flat panel liquid crystal display devices function to produce the same effects as conventional CRTs (cathode ray tubes).
It is noted that some LCDs operate on reflected light. In such cases, the light is typically reflected from an opaque back panel. However, it is also noted that both panels and their associated pixel electrodes may be made transparent so as to supply the desired optical effect by means of back lighting which is usually contained in the same physical package as the liquid crystal display itself.
It is also possible to achieve color effects in liquid crystal display devices. These color effects are achieved through the utilization of color filters arranged in registration with the pixel electrode pattern. In the past, several red/green/blue triad cluster patterns (associated with the same picture element) have been proposed for this purpose. For example, an article by S. Tsuruta et al. has indicated that improved picture quality is obtained when color pixels are arranged so the third color is positioned symmetrically above or below the other two colors. A related article by T. Saito et al. describes a matrix layout to achieve this configuration in LCD devices. In this configuration, each color pixel is divided vertically in half and a second set of vertically extending data buses is incorporated. With a transistor to address each half pixel, a staggered triad arrangement can be realized. However, a significant disadvantage of this arrangement is that the pitch of the data buses is reduced by a factor of 2 so that, for the same resolution, the photolithography is more critical and the stray capacitance effects require that a smaller fraction of the total available screen area can be used for light transmission.
A second approach that could be undertaken would be to stagger whole pixel elements on alternate lines. However, this would require the data lines to snake back and forth with half pixel jogs over half pixel dimensions. This snaking would be required for each row in the display and would result in a much larger crossover area between gate buses and data buses. This is undesirable since it increases the potential for short circuiting between gate lines and data lines in the display. Such requirements would make fabrication more difficult. Most importantly, however, such a configuration would significantly reduce the process yield, a significant economic concern. Also, short circuits between gate lines and data lines would scale linearly with crossover area. Thus, the larger the display, the greater is the possibility for circuit defects resulting in poor and/or unusable display screens.